Jelly, I'm not sure there is anything about expected losses posted in the book (and I can't check as both my copies of PP and PPLP are on loan), however, the average loss when you begin LCing is 10% of goal in the first two weeks and 5% every month there after. This is an average - people lose more, some lose less, some stall and plateau - all perfectly normal.

HTH
Nat